The present invention is directed generally to systems for displaying information, and more particularly to information display systems having selected color compensation to enhance the color of the image viewed by the user.
Handheld devices, such as handheld personal assistants, cell phones and the like, typically use Twisted Nematic (TN) or Super Twisted Nematic (STN) Liquid Crystal Displays (LCD) as the information display layer. These displays offer ease of manufacture, passive multiplexed addressing schemes, and cost structures aligned with the end application. The display usually operates in a reflective/transflective mode such that ambient light provides the primary illumination for the non-emissive display. The use of ambient illumination eliminates the need for a constantly activated system light source, which is a problem with devices that use transmissive displays, such as laptop computers. In the event of low ambient lighting, transflective displays incorporate a supplemental backlight, which is commonly user activated. This allows the device to realize smaller size, lighter weight, smaller battery size, and longer battery life, all factors important in a portable, handheld device.
A TN or STN LCD typically requires a compensation film to provide color correction due to dispersion effects within the display. Without the added compensation film, the display creates spectrally peaked light and dark states instead of the desired white and black states. STN displays may use a wide variety of design prescriptions, with a unique compensation film providing optimum performance for each design. Even with the proper compensation film however, the TN or STN display still does not provide the desired white/black performance. Instead, most common displays manifest a green/black appearance. This deficiency is attributable in large part to the spectral performance of elements within the display.
The present invention addresses the spectral deficiencies of elements in a LCD unit, and offers a system solution for performance that more closely approaches the ideal white/black display characteristic.
Generally, the present invention relates to a polarizer that has spectral characteristics particularly well suited to use in an LCD display.
One particular embodiment of the invention is directed to an optical device, comprising an absorbing polarizer having a double pass color shift of |xcex94x|xe2x89xa60.005 and |xcex94y|xe2x89xa60.005 for illumination by a C-illuminant, and a double pass contrast modulation of at least 90%.
Another embodiment of the invention is directed to an optical device, comprising an absorbing polarizer having a double pass color shift of xcex94xxe2x89xa60.005 and xcex94yxe2x89xa60.002 and a double pass contrast modulation of at least 90% under illumination by an A-illuminant. The polarizer also has a double pass color shift of xcex94xxe2x89xa60.005 and xcex94yxe2x89xa60.005 under illumination by a C-illuminant.
Another embodiment of the invention is directed to a device for displaying information, comprising two or more layers stacked together, at least one of the layers being an absorbing polarizer having a double pass color shift of |xcex94x|xe2x89xa60.005 and |xcex94y|xe2x89xa60.005 for illumination by a C-illuminant.
Another embodiment of the invention is directed to a rear projection screen having a dispersing layer stacked together with first absorbing polarizer, the first absorbing polarizer having a single pass color shift with at least one of xcex94x and xcex94y being negative under illumination by a C-illuminant, and a polarization co-efficiency greater than 90%.
The above summary of the present invention is not intended to describe each illustrated embodiment or every implementation of the present invention. The figures and the detailed description which follow more particularly exemplify these embodiments.